The CG of an airplane is far different than the proper CG for an airplane, try to be specific, because the CG could be anywhere, a proper CG is a specific point that will allow it to fly stable and balanced...it's the difference between flying and not flying...
When the weight is further from the proper CG point it is harder for the airplane to change velocity quickly. The closer the weight is to the proper CG the faster that weight can rotate around that point and change velocity. It is not as important as finding the proper CG for stable flight, as a beginner it is not something to worry very much about. Beginners usually need stable and slower reacting airplanes, not fast acting ones...besides the difference is very slight on most designs...A good rule of thumb is to simply pack all the electronics near the proper CG point, this is about all you can do with most designs as the electronics are the only things you really have an option to move around. Proper CG is almost always achieved by battery placement because it is the heaviest object on the airplane. If you wish to place the battery closer to the proper CG then you must counter balance it with lighter weight objects out on the fringe. So make sure you take into account the mass of the objects, if you place lightweight things near the edges it's not as much of an impact as placing heavier objects there, get it?